RASNZ Occultation Section - Fredegundis Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (678) FREDEGUNDIS - 2001 MAY 18

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[Prediction by Edwin Goffin]

[Prediction using OCCULT software]

The path given by Edwin Goffin crosses the Southern Ocean to the southwest of Tasmania crossing the Western Australian coastline around Esperence and again just to the north of Geraldton near local sunset. The path given by Occult lies several path widths to the southwest running from Albany to around Bunbury.

UPDATE: 17 May 2001

This prediction update has been computed by Steve Preston of the Medina, Washington (state) in the United States based on astrometry from Ron Stone of the US Naval Observatory - Flagstaff Station supplement with data from the AstDys database. The Tycho-2 position of the target star has been used.

Summary:

This updated path lies around two path widths to the southwest of the Goffin's path and just over two minutes later. It crosses the southern Western Australia coastline between Albany and Esperence (10:11 UT) running to the northwest crossing the coast again around half way between Perth and Geraldton (10:11:40 UT). Twilight will be an interference over the northern parts of this path.

Additional details of this and other events are available at Steve Preston's website at http://www.oz.net/~stevepr/Asteroids/asteroid.htm

THE EVENT AT ONE GLIMPSE:

Date and approx. UT time of event: May 18, 2001 @ 10:11 UT
Magnitude of target star: 7.0
Magnitude drop [mag]: 6.6
Estimated maximum duration [s]: 3.2
Path description: See above.
Goffin's original chart reference: A01_0530

The Occultation Path:

Approximate width [km]: 44
Uncertainty [path widths]: 1.3 (1 sigma error band)
Map: See below
Remarks: Uncertainities are given on the basis of the nominal star position errors and the expected asteroid positional accuracy.
Circles along the path are OCCULT calculated exact centerline points !!!!

Data for the target star:

Name: HIP 70945 = PPM 263046 = SAO 182611 = HL Lib
Constellation: Libra
J2000 position [h,m,s; ^o,',"]: 14h 30m 40.463s; -22^o 27' 39.30"
Position source: Tycho-2
Estimated accuracy ["]: 0.008" (0.006", 0.006")
V mag [mag]: 6.96 Slightly Variable
B-V [mag]: +0.18
Remarks:
The target star is in southeastern Libra near the borders with Virgo and Hydra. It lies 3.8 degrees northwest of 4 Librae (magnitude = 5.7). The target star is an elliptical variable with the very small brightness range of 6.93 to 7.02 with a period of 24 days.

Data for the minor planet:

Number, name: (678) Fredegundis
Approx. diameter [km]: 44.0
Source of used astrometry: US Naval Observatory - Flagstaff Station (Ron Stone), AstDys
Number of used observations: 295
Number of rejected observations: 25
Time covered by the observations: 1913 01 13 - 2001 05 12
Uncertainy Ellipse ["] (major axis, minor axis, PA): 0.029", 0.028", 70°.

Data for the event:

UT date and time of least geocentric approach: 2001 May 18, 10:07.1 UT
Approx. V mag of minor planet at event [mag]: 13.59
Geocentric parallax of minor planet ["]: 4.10
Magnitude drop [mag]: 6.6
Estimated maximum duration [s]: 3.2
Apparent motion of minor planet ["/h]: 31.99
Angular distance to moon, phase of moon [deg,%]: 136, 23%
Update computed by: Steve Preston, Medina, Washington, USA. (OrbFit)

Fredegundis Update

IMPORTANT NOTE!

Astrometric updates such as these should not be taken as definitive, but rather only as an indication of where the true track may lie relative to the original predicted track. Observers must bear in mind that later astrometry, in which the target star is measured in the same field as the asteroid, may still reveal substantial changes to the predicted track and time of the event. For this reason it is most important that observers far from the predicted track still monitor the event.

Use these links for further information:
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